Method for separating the stereoisomers of alpha-hydroxy-beta, beta-dimethylgamma-butyrolactone



Patented June 28, 1949 1 r METHOD FOR SEPARATING THE STEREO- ,ISOMERS or a-HYDROXY-fl,,6-DIMETHYL- GAMMA-BUTYROLACTONE Ralph H. Beutel, Newark, and Max Tishler, Rahway, N. J., assignors to Merck & 00., Inc., Rahway, N. J a corporation of New Jersey No Drawing. Application October 23, 194.5, 7

Serial No. 624,104

This invention relates to a method of separating stereoisomers of a-hYdIOXY-Bfi-dilflethYlgamma-butyrolactone, useful in the synthesis of pan-tothenic acid and to novel derivatives of the isomers having properties which permit their ready separation.

In accordance with one method for preparing pantothenic acid, B-alanine is condensed with the laevorotatory isomer of a-hydroxy-B,c-dimethyl-gamma-butyrolactone. The racemic lactone may be synthesized by condensing a-adimethyl acetaldehyde with formaldehyde to form a,a-dimethyl 8 hydroxy-propionaldehyde which, upon condensation withhydrocyanic acid inthe presence of calcium chloride, yields racemic a-hydroxyfi,fidimethyl-gamma butyrolactone.

Since the dextrorotatory lactone cannot be condensed with fl-alanine to produce pantothenic acid, it. is desirable that it be separated from the laevorotatory isomer.

I-Ieretofore, the racemic lactone has been resolved by converting the stereoisomers to their alkaloidal salts and separating them :b fractional crystallization. The instant process eliminated theneed for fractional crystallization and the complicated procedure and apparatus necessarily employed when the isomers are separated in this manner. According to this invention, the racemic lactone can beresolved into its optical isomers by precipitation of the double salt of brucine-dextrorotatory-a-gamma-dihydroxy-Afidimethyl-butyric acid-brucine-hydrochloride.

The reaction proceeds as follows:

H CH 5H ONa 7 Claims. (Cl. 260-236) 2 proceeds slowly at room temperature, rapidly at to C., and, when complete, a suitable acid is added to the solution in an amount slif ficient t'oneutralize any excess alkali, A stoichiometric quantity of brucine, dissolved in an in organic acid, is then added to the above solution. The alkali metal salt of the dextrorotatory agammadihydroxy--B,c-dlmethy1 butyric acid re acts with the br-ucine acid solution to form the brucine-dextrorota-tory butyric acid-brucine acid salt and the alkali metal salt of the laevorotatory" a-gamma-dihydroxy-c,c-dimethyl butyric acid remains in solution.

The double salt is formed immediately. The brucine hydrochloride solution is heated to- 80 C. to enact-complete solution at the concentration employed. The two solutions are mixed hot and then allowed to cool down to effect the proper crystallization of the double salt. Equivalent molecular amounts of brucine and the racemic l-actoneshould be employed in the reaction if a maximum yield of the double salt is to be obtained. Anystrong inorganic acid may be used as the acid moiety of the complex but hydro chloric acid is preferred. Apparently brucine is a critical constituent. Tests indicate that alka loids such as quinine, cinchonine, thebain, etc'., do not give double salts under the conditions used to prepare the brucine double salts.

The optical configuration in the case of" the a-hydroXy-c,c-dimethy1 gamma butyrolactone and a-gamma-dihydroxy-,8,c-dimethy1 butyric acid is unknown at present. Dextrorotatory a-.

gamma-dihydroXy-fl,fi-dimethy1 butyric acid gives rise to the laevorotatory lactone and vice versa. In order, therefore, to obtain the pure laevorotatory form of a-hydroxy-fl,c-dimethylgamma-butyrolactone, it is necessary to treat the brucine-dextrorotatory form of a-gamma-dihydroxyc,fi-dimethyl butyric acid-brucine hydrochloride with a base and extract with chloroform or the like to remove the alkaloid.

The following example sets forth a method of carrying out the invention, but it is to be understood that it is given by way of illustration and not of limitation.

Example About 2.6 g. (.02 mole) of racemic a-hydroxyp,;3-dimethyl-gamn1a-butyrolactone is dissolved in approximately 20 cc. of 1.04 N sodium hydroxide and heated on a steam bath for 15 minutes. Any excess sodium hydroxide present in the solution is then neutralized with hydrochloric acid.

droxy-p,p-dimethyl butyric acid. The reaction 56 This solution, containing the racemic sodium salt of a-gamina-dihydroxy-p,p-dimethyl butyric: acid, is then added to a solution of 9.32 g. (.02' mole) of brucine dissolved in a mixture of 24 cc. of hot water and 8 cc. of 2.5 N hydrochloric acid. The reaction is carried out at approximately 80 C. The solution is cooled in ice, seeded and permitted to stand for several hours. The crystalline material which is formed is removed from the supernatant liquid, washed with a small amount of ice Water and dried overnight at room temperature. The product is the double salt corresponding tobrucine dextrorotatory-u-gamma-dihydroxy-p,- p-dimethyl butyric acid-brucine-hydrochloride; of -11.8 (0.1 g. in cc. chloroform).

To obtain pure laevorotatory oz-hYdIOXY-Bfidimethyl-gamma-butyrolactone, the double salt obtained above is treated with a base such as aqueous sodium hydroxide and extracted with chloroform, ethylene dichloride or the like to remove the alkaloid. The alkali extract, containing the lactone is then extracted with ether, acidified, heated on a steam bath, cooled, saturated with ammonium sulfate and extracted with chloroform. Laevorotatory a-hydroxy-p,p-dirnethylgamma-butyrolactone possessing the rotation [a] -47.0 in 2% water, is obtained when the extract is dried over sodium sulfate and concentrated in vacuo to dryness.

Modifications may be made in carrying out the invention without departing from the spirit of our invention or the scope of the subjoined claims.

This application is a continuation-in-part of our earlier application, now Patent No. 2,390,281.

We claim:

1. The process that includes the step comprising reacting racemic u-hydroxy-fl,fl-dimethylgamma-butyrolactone with alkali to form the alkali metal salts of racemic a-gamma-dihydroxy- B B-dimethyl butyric acid, treating the alkali metal salts with approximately 1 molar equivalent of brucine dissolved in an inorganic acid and removing the brucine-dextrorotatory-u-gammadihydroxy-p,p-dimethyl butyric acid-brucineacid salt formed.

2. The process that includes the step comprising reacting racemic a-hydroxy-p,,13-.-dimethylgamma-butyrolactone with an aqueous sodium hydroxide solution to form the sodium salts of racemic a-gammadihydroxy-p,p-dimethyl butyric acid, treating the sodium salts with approximately 1 molar equivalent of brucine dissolved in hydrochloric acid and removing the brucinedextrorotatory-w-gamma-dihydroxy-p,fl-dimethyl butyric acid-brucine-hydrochloride formed.

3. The process that includes the step comprising reacting an alkali metal salt of racemic ozgamma-dihydroxy-p c-dimethyl butyric acid with a solution of approximately 1 molar equivalent of brucine dissolved in an inorganic acid and removing the brucine-dextrorotatory-a-gamma-dihydroxy-flfi-dimethyl butyric acid-brucine-acid salt wherein X is halogen.

6. A composition of matter represented by the formula droxy-p,p-dimethyl butyric acid-brucine-hydrm: chloride salt having a [a] of approximately 11.8 (0.1 g. in 5 cc. chloroform).

RALPH I-I.- BEUTEL. MAX TISHLFER.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,319,545 Harris et al. May 18, 1943 2,328,000 Finkelstein Aug. 31, 1943 2,390,281 Tishler et al. Dec. 4, 1945- 

